The dowels of the referenced type have some drawbacks that can be improved in various aspects, such as the increase in the degree to which the dowel is packed into the insertion hole in the inside wall, outside wall or facing; ensuring, at the time of insertion, the position and centring of the clamp in the dowel head before laying any cables, bundle of cables or conduit; ensuring the direction of the dowel in the insertion hole prior to inserting said dowel into the inside wall, outside wall or facing; increasing the versatility of the dowel so that just one single model for each diameter in the dowel range can be used indistinctively in solid brick or hollow inside walls or outside walls; the degree of flexibility of the annular retention tabs; and the subsequent adoption of the cylindrical configuration for the central core.